Method and device for chromatography comprising a concentration step

ABSTRACT

The invention concerns a method for multiple-column chromatographic spearation producing at least two fractions, comprsing the following steps: in output of the extract, zone 1, or the raffinate zone, zone III: (i) drawing at least part of the output flow of said zone; (ii) concentrationg said part; and (iii) re-injecting at least partly said concentrated part. The invention also concerns a device for implementing said method.

The present invention relates to a process and apparatus forchromatography, allowing improved productivity.

Preparative chromatography is employed as a method for purifyingmixtures, in particular pharmaceutical mixtures. For example,present-day chromatography methods can be schematized as the separationof two or several “components” of a feed or mixture to be purified.Using a solvent and a chromatography bed, two or more fractions areobtained. In one particular mode, two fractions are obtained the firsthaving a first “component” and the other a second “component”. One ofthe two, and more rarely both, component(s) is/are the one(s) lookedfor.

Several chromatography techniques on an industrial scale are known,including the multi-column SMB (simulated moving bed) and Varicol®types.

The SMB process calls on the use of simulation of counter-flow of thebed and fluid, notably by application of the technology initiallydeveloped by UOP (U.S. Pat. Nos. 2,985,589, 3,291,726 and 3,266,604).Thus, the points of introduction of the feed and eluting agent areperiodically displaced, as are the points at which the extract andraffinate are drawn off. Displacement is synchronous, meaning that thevarious feed and draw-off points are displaced simultaneously.

The so-called Varicol® process which is fundamentally different fromSMB, employs asynchronous displacement of the various feed and draw-offpoints. We can mention that this apparatus and the process associatedtherewith are notably disclosed in International ApplicationWO-A-0025885. That document discloses a separation method for at leastone component from a mixture containing it, in apparatus having a set ofchromatography columns or sections of chromatography columns containingan absorbent, arranged in series and in a loop, the loop having at leastone feed injection point, a point for drawing-off the raffinate, a pointfor injecting an eluting agent and a point for drawing-off the extract,in which a chromatography zone is determined between an injection anddraw-off point or vice-versa, the process being characterised in that atthe end of a given time period, all the injection and draw-off pointsare shifted by the same number of columns or column sections,advantageously by one column or columns section, in a given directiondefined with respect to that of the flow of a main fluid circulatingthrough the loop and in that, during said period, the various injectionand draw-off points are shifted at different points in time whereby thelength of the zones defined by said different points is variable.

Both the above techniques call on the use of a multi-column process theperformance of which is a limiting factor as regards a process that iscompetitive with conventional purification techniques (for example,crystallization, extraction, etc).

Further, the productivity of a chromatography process is generallylimited by the capacity of the chromatographic carrier (number ofabsorption sites on the carrier). The majority of preparativechromatographic applications involve the use of injection conditions forwhich the effects of overload are felt: the amount injected is maximizedup to the point where the effects of saturation of the carrier limitseparation of the species injected.

There is consequently a need to improve the performance of multi-columnsystems, either through greater productivity for identical purity of thepurified products or through higher purity of the products with anidentical injected amount.

U.S. Pat. No. 5,387,347 discloses a multi-column process implementing aconcentration step. This step involves drawing off part of the liquidcirculating corresponding to at least twice the feed throughput. Thisdrawing off (without reinjection), is implemented immediately prior toinjecting the feed.

There is nothing in that document teaching or suggesting the presentinvention.

The invention thus provides a multi-column chromatography separationprocess producing at least two fractions, comprising the followingsteps, at the outlet from the extract zone, zone I, or raffinate zone,zone III: (i) at least a part of the outlet flow rate from said zone isdrawn off; (ii) said part is concentrated; and (iii) the concentratedpart is at least partially reinjected.

According to one embodiment, the totality of the outlet flow rate fromsaid zone is drawn off.

According to another embodiment, the concentrated part is partiallyreinjected.

According to another embodiment, between 50 and 99.5% of theconcentrated part, preferably between 70 and 98%, is reinjected.

Alternatively, the concentrated part is totally reinjected.

According to one embodiment, a concentration factor F is comprisedbetween 1.1 and 10, preferably between 1.25 and 5.

According to another embodiment, drawing-off is performed downstream ofthe extract zone, zone I.

In one embodiment, the chromatography separation is of the SMB type.

In another embodiment, the chromatography separation is of the Varicoltype.

There is also provided chromatography apparatus comprising: (i) aplurality of separation columns; (ii) a drawing off point at the outletfrom said columns for drawing off at least a part of the outlet flowrate from a column; a device for concentrating said part; (iii)areinjection point immediately after the drawing off point forreinjecting at least partially the concentrated part.

The apparatus preferably comprises a valve between the drawing-off andreinjection points.

In one embodiment, the apparatus comprises partial collection of theconcentrated part.

According to another embodiment, the concentration device is anevaporator.

In one embodiment, the plurality of separation columns is of the SMBtype.

In an alternative embodiment, the plurality of separation columns is ofthe Varicol type.

The apparatus is adapted for carrying out the process of the invention.

Further characteristics and advantages of the invention will now bedescribed in detail below with reference to the attached drawings inwhich:

FIG. 1 is a diagrammatic view of an actual continuous counter-currentchromatographic process: the “true moving bed”,

FIG. 2 is a diagrammatic view of apparatus of the invention.

With reference to FIG. 1 a conventional 4-zone counter-flow process,i.e. the “true moving bed” is described. According to that principle,the solids rotate continuously in a closed loop between fixed points forintroducing the feed, eluting agent and for drawing off the extract andraffinate. The following four zones are then distinguished:

-   -   zone 1: everything located between the eluting agent and extract        lines;    -   zone 2: everything located between the extract and feed lines;    -   zone 3: everything located between the feed and raffinate lines;        and

Zone 4: everything located between the raffinate and eluting agentlines.

The solid flow rate is constant throughout the system but, in view ofthe inlet/outlet flow rates, the liquid flow rate varies depending onthe zone: QI, QII, QIII and QIV being the respective flow rates in thezones I, II, III and IV.

The principle of the simulated moving bed, reviewed briefly above,operates by shifting the inlet and outlet points at fixed intervals in amulti-column system. This process is defined by the following maincharacteristics:

1. Zones defined by the position of the inlet/outlet lines;

2. A fixed number of columns per zone;

3. Fixed length zones; and

4. Synchronized displacement of all the inlet/outlet lines.

(The characteristics 2, 3 and 4 are due to the fact that the simulatedmoving bed simulates the behavior of the “true” moving bed).

In the so-called Varicol® process, the basic idea is to modify the truemoving bed discussed above with an aim to allowing variation over timeof zone length.

Contrary to the true moving bed, zone lengths are no longer fixed butvary over time. In one embodiment, these variations can be periodic sothat the system comes back to its original position after a given time.(Due to variation in zone length, unlike the “true” moving bed, thissystem is not stationary and solid speed is not constant with respect tothe inlet/outlet lines).

When a Varicol® process is implemented, zone lengths oscillatecontinuously by one column, the increase in the length of one zone beencompensated for by decrease in that of the next one. For otherimplementations, increase in length of one zone can for example becompensated for by a decrease in the opposite zone, but otherimplementations are possible.

The differences between the Varicol® system and the simulated moving bedprocess are then:

1. Zone lengths are not constant;

2. Column number per zone is not constant over time;

3. The inlet/outlet lines are not displaced simultaneously;

4. Solid flow rate simulated by the Varicol® process is not constantwith respect to the inlet/outlet lines.

As explained, a preferred implementation of the Varicol process isperiodic (period Δt), so that after a given time, this system returns toits original configuration. During this time, the number of columns ineach zone has been varied, and for commodity purposes, it can be usefulto define a mean number of columns per zone:

<Nb1>: mean number of columns contained in zone 1 during one period

<Nb2>: mean number of columns contained in zone 2 during one period

<Nb3>: mean number of columns contained in zone 3 during one period

<Nb4>: mean number of columns contained in zone 4 during one period.

Similarly, a simulated moving bed system can be represented by:SMB: Nb1/Nb2/Nb3/Nb4

The Varicol® system can be represented by:VARICOL® <Nb1/<Nb2>/<Nb3>/<Nb4>

(Nevertheless, whereas the number of columns per zone has a real meaningfor SMB systems, the mean numbers (generally not whole numbers) have notechnical meaning and are simply employed for commodity purposes for theVaricol process).

With reference to FIG. 2, apparatus comprising six columns is described.Zones I, II, III and IV are defined between the various points ofinjection and drawing-off, as indicated above. The apparatus accordingto the invention comprises a break in the column loop. One could alsoonly have a partial loop break. This can be typically managed using avalve located between the draw-off and injection points.

The flow collected at the outlet from the column located upstream of thepoint where the loop is broken is continuously or discontinuouslyconcentrated, for example using an evaporation process. The concentratedsolution is then partially (for example between 50 and 99.5%, preferably70-98%) or totally reinjected to the inlet to the column downstream ofthe break point. This break point is regularly switched in order topreserve the same position relative to the zones of the process. Thereinjection rate is defined with respect to the fractions. The break inthe loop with a view to performing concentration can also be applied tomulti-column processes already having a break in the loop at any pointwhatsoever.

According to the method of concentration used, the flow collected,concentrated and reinjected may necessitate readjustment of thecomposition in eluting agent (for example, if the latter is not a puresolvent).

In the case of FIG. 2, the break is downstream of zone I. Thisembodiment is advantageous notably in the particular case of a Langmuirtype absorption isotherm having a competitive saturation effect for thenumber of sites on the chromatographic carrier. The flow collected isthen concentrated and partially reinjected into the column downstream(inlet to Zone II). That fraction of the concentrated flow which is notreinjected is collected: it corresponds to concentrated extract (mostretained product purified).

In the case illustrated (break in loop downstream of zone I), the newprocess is characterised by the concentrated flow concentration rate F:

-   -   F=C_(extconc)/C_(outZoneI) (C_(extconc) and C_(outZoneI) being        the concentrations of the concentrated extract collected and of        the outlet flow from zone I, respectively). (C_(extconc) is also        the concentration of the injection flow to zone II).    -   the eluting agent, feed and raffinate flow rates: Q_(elu),        Q_(feed) and Q_(raf), respectively (the extract flow rate in a        conventional process would be Q_(ext))    -   the input flow rate to zone II, Q_(II).    -   the outlet flow rate from zone I, Q_(I).

The concentrated extract flow rate collected (Q_(extconc)) is now givenby the material balance on the process, as follows:Q _(extconc)=(Q _(elu) +Q _(feed) −Q _(raf))/F+Q _(II)*(1/F−1)(or also Q _(extconc) =Q _(I) /F−Q _(II))

The reinjection rate T indicated above is given by:T=(Q _(II) *F)/Q _(I)(or also T=1−(Q _(extconc) *F)/Q _(I))q. This factor F can vary between1.1 and 10, preferably between 1.25 and 5.

The disclosed process allows separation of binary mixtures. It isconsequently particularly adapted to separation of enantiomers or to anyother application designed to separate a mixture of two species.

The process can also be applied to mixtures of more than two species.The mixture is then separated into two fractions at each step in the newprocess. Depending on requirements, several purification steps, by a newprocess or another process, can be implemented.

The process according to the invention is generally continuous; the flowrates given above are constant over time.

In certain cases, one can also be led to reduce or stop, over a fractionof the period, the extract or raffinate flow rate while simultaneouslydecreasing the eluting agent flow rate. This can be achieved since:

-   -   as the lines for injecting eluting agent and drawing-off extract        are located at the same point (column number in Zone I        temporarily zero, which can happen when the number of columns is        small and the offset of feed and draw-off lines is performed        asynchronously, in the case of the Varicol process): the        collection of extract can then be reduced or stopped and the        eluting agent flow rate diminished by the same amount;    -   the line for injecting eluting agent and drawing off raffinate        are located at the same point (number of columns in zone IV        temporally 0) : raffinate collection can be reduced or stopped        and the flow rate of eluting agent decreased by the same amount.

This allows, in certain cases, the dilution of what is collected to bedecreased thereby reducing eluting agent consumption for the process(amount of solvent employed for purifying a given amount of product).

Conventionally, the eluting agent employed in the process can be aliquid, a super-or sub-critical fluid or a compressed gas.

The present process applies to any type of chromatography process,including those that couple reaction and separation. An example of sucha process is disclosed in United States Patent Application2001/0031903A1.

The following examples illustrate the present invention without howeverlimiting the scope thereof.

EXAMPLE 1

The separation of the enantiomers of Ketoprofene was performed firstlyusing SMB and secondly using the process of the invention. We show thatthe new process makes it possible either to obtain higher purity atconstant productivity, or to increase productivity at constant purity.

Separation is performed on a continuous multi-column pilot employing six1×10 cm diam. columns filled with 20 μm ChiralCel OJ (Daicel). Theeluting agent was a hexane/IPA/acetic acid mixture 90/10/0.5% v/v.

Racemic solubility in the eluting agent was around 25 g/l at ambienttemperature.

Separation took place at 25° C., optical purity of 99% was aimed at forthe extract and raffinate.

Column distribution, both in SMB and in the process of the invention,was as follows:

-   -   one column in zone I,    -   two columns in zone II,    -   two columns in zone III,    -   one column in zone IV.

Performance Obtained with SMB

The conditions are given in the table below. Feed conc Q_(feed) Q_(elu)Q_(ext) Q_(raf) (g/l) (ml/min) (ml/min) (ml/min) (ml/min) Q_(I) (ml/min)25 0.74 23.81 18.10 6.44 38.54

The switch-over period was 1.07 minutes.

Optical purities obtained were 99.0% for the extract and 95.3% for theraffinate with a productivity of 26.6 g racemic injected per day.

Performance Obtained with the Process of the Invention

Case A

The conditions are given in the table below (the recycling flow rate isnot indicated since the loop is open). Feed conc Q_(feed) Q_(elu)Q_(raf) Q_(II) (g/l) (ml/min) (ml/min) F (ml/min) (ml/min) 25 0.74 23.801.90 4.49 18.50

The switch-over period was 1.07 minutes.

Optical purities obtained were 99.4% for the extract and 98.4% for theraffinate for a productivity of 26.6 g racemic injected per day. We cannote an improvement both in extract purity and raffinate purity comparedto the optimized SMB process for the same productivity.

Case B

The conditions are given in the table below. Feed conc Q_(feed) Q_(elu)Q_(raf) Q_(II) (g/l) (ml/min) (ml/min) F (ml/min) (ml/min) 25 1.13 23.791.89 3.77 19.26

The switch-over period was 0.95 minutes.

Optical purities obtained were 99.1% for the extract and 95.50% for theraffinate for a productivity of 40.7 g racemic injected per day. We cannote a 50% increase in productivity compared to the SMB process,accompanied by a slight improvement in raffinate purity.

The table below summarizes the flow rates in the various zones. Flowrate SMB Case A Case B Q_(I) 38.54 38.54 40.41 Q_(II) 20.44 18.50 19.26Q_(III) 21.18 19.24 20.39 Q_(IV) 14.74 14.75 16.62 Q_(extconc) 1.77 2.13T 91 90

1. A multi-column chromatography separation process producing at leasttwo fractions, comprising the following steps, at the outlet from theextract zone, zone I, or raffinate zone, zone III: (i) at least a partof the outlet flow rate from said zone is drawn off; (ii) said part isconcentrated; and (iii) the concentrated part is at least partiallyreinjected.
 2. The process according to claim 1, in which the totalityof the outlet flow rate from said zone is drawn off.
 3. The processaccording to claim 1, in which the concentrated part is partiallyreinjected.
 4. The process according to claim 3, in which between 50 and99.5% of the concentrated part, preferably between 70 and 98%, isreinjected.
 5. The process according to claim 1, in which theconcentrated part is totally reinjected.
 6. The process according toclaim 1, in which a concentration factor F is comprised between 1.1 and10, preferably between 1.25 and
 5. 7. The process according to claim 1,in which drawing-off is performed downstream of the extract zone, zoneI.
 8. The process according to claim 1, characterised in that thechromatography separation is of the SMB type.
 9. The process accordingto claim 1, characterised in that the chromatography separation is ofthe Varicol type.
 10. Chromatography apparatus comprising: i. aplurality of separation columns; II. a drawing-off point at the outletfrom said columns for drawing off at least a part of the outlet flowrate from a column; III. a device for concentration said part; IV. areinjection point immediately after the drawing-off point forreinjecting at least partially the concentrated part.
 11. The apparatusaccording to claim 10, comprising a valve between the drawing-off andreinjection points.
 12. The apparatus according to claim 10, comprisingpartial collection of the concentrated part.
 13. The apparatus accordingto claim 10, in which the concentration device is an evaporator.
 14. Theapparatus according to claim 10, characterised in that the plurality ofseparation columns is of the SMB type.
 15. The apparatus according toclaim 10, characterised in that the plurality of separation columns isof the Varicol type.
 16. (canceled)